Metallic flat gasket and a method for production of same

ABSTRACT

A flat gasket including a sealing plate having a media-passage opening, a spring steel functional layer with a sealing bead surrounding the media-passage opening, and a second sealing layer formed of a deformable second steel sheet, which has an original thickness and an original hardness and around the media-passage opening forms an annular zone, which has at least one annular region that is thickened compared with the original thickness and forms an annular groove for engagement of the sealing bead, wherein the second sealing layer in the thickened annular region has a greater hardness than the original hardness, and wherein the annular zone has (a) one thickened annular region, into which an annular groove is impressed on at least one side of the second sealing layer, or (b) in the radial direction relative to the media-passage opening, two thickened annular regions spaced apart to form the annular groove between them.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of international applicationnumber PCT/EP2014/057954 filed on Apr. 17, 2014, which claims priorityto German patent application number 10 2013 104 269.4, filed Apr. 26,2013, the entire specification of both being incorporated herein byreference.

FIELD OF THE INVENTION

The invention relates to a metallic flat gasket comprising a sealing orgasket plate having at least one media-passage opening and having, inthe region of the media-passage opening, at least one spring steelfunctional layer formed of a first steel sheet with a sealing bead thatsurrounds the media-passage opening and is formed as a full bead with abead crest arranged between two bead feet, and also a second sealing orgasket layer, which is directly adjacent to the functional layer and isformed of a second steel sheet, which can be deformed more easilycompared with spring steel, which second sealing layer has, around themedia-passage opening, an annular zone adjacent thereto and, radiallyoutwardly adjacently to said annular zone relative to the media-passageopening, has an original thickness and an original hardness of thesecond steel sheet, wherein the second sealing layer in the annular zonehas at least one annular region that is thickened compared with theoriginal thickness of the second steel sheet, which thickened annularregion extends along the sealing bead in a plan view of the sealingplate.

The invention also relates to a method for producing a flat gasket ofthis type.

BACKGROUND OF THE INVENTION

In the case of a flat gasket of this type with a multi-layer sealingplate, the media-passage opening naturally extends through all sealinglayers that the sealing plate has in the region of this media-passageopening.

A spring steel is to be understood to be a steel in which the ratio ofyield point R_(e) or alternatively elastic limit R_(p0.2) to tensilestrength R_(m) is greater than 0.85 (85%).

A functional layer is understood by a person skilled in the art ofgaskets to mean a sealing layer having at least one bead, which can beat least substantially reversibly flattened when the flat gasket isinstalled between mutually opposed surfaces of components that are to besealed with respect to one another, but particularly during operation ofthe flat gasket, such that the height of the bead, starting from thestate thereof when the flat gasket is not pressed, is reduced, whereinthe spring steel sheet of the functional layer is deformed at leastsubstantially only in the elastic region of the spring steel.

Depending on the design, dimensioning and arrangement of the thickenedannular region of a flat gasket of the type in question and alsodepending on the design and thickness of the second sealing layer, aperson skilled in the art of gaskets will understand this to mean aspacer layer and/or what is known as a stopper layer and/or what isknown as a carrier sheet, which determine and/or increase the thicknessof the flat gasket in the installed state, wherein the following shouldbe noted in this regard: Particularly in the case of flat gaskets of thetype in question for internal combustion engines, the media-passageopening of these gaskets being intended for the hot and pressurizedcombustion gases, the gasket fabricator often seeks to form the flatgasket, therefore in particular a cylinder head gasket, such that thecompressive forces acting on the installed flat gasket are highlyconcentrated on the sealing plate region directly bordering themedia-passage opening and surrounding said opening, for which reasonthis sealing plate region is designed such that the elements of thesealing plate arranged in said region one above the other when the flatgasket is installed are pressed en bloc, and there the sum of thematerial thicknesses of the aforementioned sealing plate elements isgreater than in a sealing plate region arranged further radiallyoutwardly relative to the media-passage opening—in the case of acylinder head gasket and a media-passage opening serving as a combustionchamber opening, a person skilled in the art of gaskets will refer to agasket portion of increased thickness surrounding the combustion chamberopening. It is also noted that in the case of flat gaskets of the typeunder discussion a deformation limiter (usually referred to as astopper) is often associated with the sealing bead and has the task ofprotecting the sealing bead, during operation of the flat gasket,against an excessive flattening, but particularly against an excessivelyhigh time variation (dynamic) of the bead height, i.e. protectingagainst deformation of the spring steel sheet of the functional layer inthe resilient region of the spring steel during the course of the timevariation of the bead height, and also against significant plasticdeformation of the spring steel. In this context it is noted that, wheninstalling a flat gasket of the type under discussion, i.e. as the flatgasket is clamped between two components that are to be sealed withrespect to one another, such as a cylinder head and an engine block, thefunctional layer consisting of a spring sheet steel, in the region of asealing bead, is not only deformed in the resilient region of the springsteel, but is also plastically deformed to a small extent, such that,following the expansion of a flat gasket, the sealing bead has a heightthat is slightly smaller than the original bead height. It should alsobe mentioned that, when, in the case of a flat gasket of the type underdiscussion, the stopper is arranged on the second sealing layer, this isusually referred to as a stopper layer.

U.S. Pat. No. 6,499,743 B2 discloses a triple-layer metallic cylinderhead gasket comprising two outer functional layers and an inner sealinglayer arranged therebetween and referred to as a carrier layer, which isto serve to provide a gasket portion of increased thickness and also isto perform a stopper function for the two functional layers, whereinthis cylinder head gasket is intended and designed for what is known asan engine with cylinder liners, in which a cylinder liner enclosing eachcombustion chamber is inserted into the cylinder block for each of saidcombustion chambers. The two functional layers each have, above eachcylinder liner, a sealing bead that runs around the combustion chamberconcerned and that is formed as a full bead, wherein the two sealingbeads lie one above the other in the axial direction of the cylinderliner and protrude in the direction of the carrier layer, i.e. they abutwith their bead crests against the carrier layer when the cylinder headgasket is installed. Irrespective of the fact that the carrier layer foreach combustion chamber has two thickened annular regions with roundcross section, the carrier layer has the same sheet thickness everywhereand therefore has two flat main surfaces that are parallel to oneanother. A thickened annular region arranged radially inwardly relativeto the combustion chamber borders the combustion chamber directly andlies (as considered in the direction of the axis of the cylinder liner)above the cylinder liner and radially inwardly of the sealing beads at aradial distance from the latter, which are likewise arranged above thecylinder liner, and in accordance with the basic principle of U.S. Pat.No. 6,499,743 B2 the radially inner thickened annular region above thecylinder liner is to gasket the gasket gap between the cylinder head andthe cylinder block provided with the cylinder liner, i.e. the radiallyinner thickened region forms a gasket portion of increased thickness.The radially outer thickened annular region is arranged radially outsidethe sealing beads and the cylinder liner above the cylinder block and inaccordance with the basic principle of U.S. Pat. No. 6,499,743 B2 is tolimit the compressive forces acting on the sealing beads of theinstalled cylinder head gasket. The way in which the carrier layer is tobe provided with the two thickened annular regions cannot be derivedfrom U.S. Pat. No. 6,499,743 B2.

A further triple-layer metallic cylinder head gasket comprising twoouter functional layers and an inner sealing layer arranged therebetweenand referred to as a spacer layer is presented in EP 1 271 016 B1, andin this known cylinder head gasket as well the sealing beads of thefunctional layers each surrounding a combustion chamber opening protrudein the direction of the inner sealing layer, i.e. the spacer layer. Inthis cylinder head gasket a height-profiled stopper, i.e. a stopper thatin the peripheral direction of the adjacent combustion chamber openinghas a height profile, i.e. different heights and/or thicknesses (seeparagraph [0005]), is to be produced with minimal outlay for a sealingbead of a functional layer or the sealing bead of each functional layer.For this purpose an auxiliary sheet in the form of a sheet ringsurrounding the respective combustion chamber opening is provided on theside of the spacer layer facing towards the respective functional layerand, as considered in the direction of the axis of the combustionchamber opening, extends radially outwardly from the combustion chamberopening edge until beyond the sealing bead and is pressed by embossinginto the spacer layer via an annular region which is opposite thesealing bead in question and of which the radial width is slightlygreater than the radial width of the sealing bead, more specificallywith the formation of likewise annular indentations corresponding to oneanother in the spacer layer and in the auxiliary sheet. Annular regionsof the auxiliary sheet, which abut the spacer layer outside theindentations and are each provided by the embossing process by means ofan accordingly shaped embossing tool with a height profile, morespecifically together with the spacer layer, radially inside andradially outside the sealing bead are in turn formed in this way (in aplan view of the cylinder head gasket) on each side of the sealing beadand of the indentations, such that these regions radially inside andradially outside the sealing bead each form a height-profiled stopperfor the sealing bead, which, when the cylinder head gasket is pressed,engages via its bead crest in the indentation of the auxiliary sheet—inthis case a person skilled in the art of gaskets will refer to a doublestopper for the sealing bead. As is clear from FIG. 2 in conjunctionwith paragraph [0016] of EP 1 271 016 B1, the spacer layer, of which thethickness is a multiple of the thickness of the auxiliary sheet, isplastically deformed during the embossing process, both in the region ofthe indentation of said spacer layer and between this indentation andthe combustion chamber opening. It is essential that the spacer layerdoes not at any point have a thickened annular region, but also does notat any point of its region provided with the auxiliary sheet have athickness that is greater than the original thickness of the spacerlayer, specifically the thickness thereof radially outside the auxiliarylayer.

DE 195 48 237 A1 presents a further triple-layer cylinder head gasketcomprising two functional layers and a spacer layer arrangedtherebetween, towards which the sealing beads of the two functionallayers protrude. In order to be able to adjust what is known as theinstallation thickness, i.e. the thickness of the cylinder head gasketonce this has been installed, without the use of differently formedfunctional layers, more specifically only by the use of spacer layers ofdifferent thickness, the spacer layer has a thickened annular regionaround a combustion chamber opening and directly bordering same, inwhich thickened annular region the spacer layer is thicker than in itsother regions, and in addition the spacer layer has, radially outsidethis thickened annular region and on each of the two sides thereof, anannular groove, with which the sealing bead of the adjacent functionallayer engages via its bead crest when the cylinder head gasket ispressed. As is clear from DE 195 48 237 A1 (see FIGS. 2 to 4 thereof andalso column 1, lines 59 to 62), this thickened annular region providedon the spacer layer is produced either in that the actual spacer layeris deformed by forging, i.e. the spacer layer is deformed in the hotstate of the metal, or the spacer layer is provided with annularoverlays or a sheet layer is placed on the spacer layer and is foldedback on itself around the combustion chamber opening and directlybordering said opening. This known cylinder head gasket thus has only asingle thickened annular region bordering the combustion chamberopening, and this thickened annular region serves in this cylinder headgasket to produce a gasket portion of increased thickness and inaddition is to prevent the sealing beads from being able to be pressedflat.

SUMMARY OF THE INVENTION

The problem addressed by the present invention is that of forming ametallic flat gasket of the type defined in the introduction, for thesecond sealing layer of which a relatively ductile and therefore easilydeformable steel sheet is used, such that said flat gasket via itssecond sealing layer forms a double stopper for the sealing bead of theat least one functional layer, which double stopper is very resistant todeformation in respect of the compressive forces acting on the installedflat gasket (in the direction perpendicular to the sealing plate plane)and can preferably be produced such that relatively little space isrequired for the double stopper in the radial direction relative to themedia-passage opening (particularly in the case of flat gaskets, inparticular cylinder head gaskets, for modern internal combustion enginesthere is often insufficient space for a conventional double stopperbetween the media-passage opening and a passage opening or a pluralityof passage openings adjacent thereto).

Proceeding from a metallic flat gasket of the type defined in theintroduction, this object can be achieved in accordance with theinvention in that the at least one thickened annular region, on the sideof the second sealing layer facing towards the functional layer, formsan annular groove, in which the sealing bead engages with its bead crestwhen the flat gasket is pressed, wherein the second sealing layer in theat least one thickened annular region produced by deforming somesections of the second steel sheet has a greater hardness, based on astrain hardening in some sections of the second steel sheet on accountof the deformation, than the original hardness of the second steelsheet, and wherein

-   -   (a) the annular zone has only one thickened annular region, in        which an annular groove is impressed on at least one side of the        second sealing layer, or    -   (b) the annular zone has, in the radial direction relative to        the media-passage opening, two thickened annular regions        arranged one behind the other and spaced apart from one another        which form the annular groove between them.

As will become clear from the following description, the flat gasketaccording to the invention comprising an annular zone according to theabove-mentioned feature (a) and/or comprising an annular zone accordingto the above-mentioned feature (b) is characterized in preferredembodiments in that the second sealing layer is cold-formed in itscorresponding layer region or its corresponding layer regions in orderto produce the thickened annular region or the thickened annular regionsand is thus provided with a hardness (specifically on account of astrain hardening) in this layer region or in these layer regions that isgreater than the original hardness of the second steel sheet.

Where reference is made above to the fact that when the flat gasket ispressed the sealing bead engages with its bead crest in the annulargroove, this may also mean that when the gasket is pressed the sealingbead lies only over part of its height within the annular groove. Thiscould be the case when, with the flat gasket installed, the sealing beadis in what is known as a main pressure path (in which it provides asealing function and also transfers forces) and the double stopper isnot pressed in each phase of the sealing operation, i.e. does not bearcontinuously against the adjacent functional layer on one or both sidesof the sealing bead. If, by contrast, the gasket is in what is known asa shunt pressure path (in which it provides solely a sealing function),the double stopper is usually always pressed on both sides against theadjacent functional layer in each phase of the sealing operation.

If, in the case of the flat gasket according to the invention the secondsealing layer has two thickened annular regions arranged at a radialspacing from one another and produced independently of or separatelyfrom one another, it has, between these annular regions, preferably atleast approximately the original thickness and also the originalhardness of the second steel sheet; in such an embodiment the secondsealing layer has at least substantially not been deformed between thethickened annular regions—between the thickened annular regions there isno need for an increased hardness of the second sealing layer caused bya strain hardening.

When producing multi-layer metallic cylinder head gaskets comprising twofunctional layers and a further sealing layer arranged therebetween,towards which further sealing layer a sealing bead of the two functionallayers enclosing a combustion chamber opening protrudes, it is alreadyknown to form the further sealing layer as a stopper layer, which has(in a plan view of the cylinder head gasket), between the combustionchamber opening and the sealing beads of the two functional layersarranged above one another, a thickened annular region enclosing thecombustion chamber opening and acting as a stopper for the sealing beads(see DE 10 2006 021 499 A1), wherein, for the further sealing layer, asteel sheet that can be more easily deformed compared with the springsteel of the functional layers is used and is provided with thethickened annular region as follows.

In a first embodiment of the production method from DE 10 2006 021 499A1 a temporary passage opening concentric with the combustion chamberopening to be provided in the further sealing layer is formed in thesteel sheet for said further sealing layer, the diameter of said passageopening being smaller than that of the combustion chamber opening,whereupon the steel sheet is compressed from the edge of the temporarypassage opening such that the steel sheet, in an annular zone borderingthe aforementioned edge, obtains a greater thickness than the originalthickness of this steel sheet in order to produce a blank of thethickened annular region, whereupon this blank is brought by means ofembossing into the form of the thickened annular region (see FIGS. 4A to4D of DE 10 2006 021 499 A1). The thickened annular region serving as astopper then has a substantially rectangular cross section and protrudesbeyond both primary surfaces of the further sealing layer, which is flatfor the rest and has the same thickness everywhere.

In a second embodiment of the known production method as well, atemporary passage opening concentric with the combustion chamber openingto be produced is formed in the steel sheet used for the further sealinglayer, the diameter of said passage opening being smaller than that ofthe combustion chamber opening, whereupon a bead-like bulge enclosingthe temporary passage opening annularly is impressed into the steelsheet such that here the outer edge of the temporary passage opening isdrawn radially outwardly, whereupon the region of the steel sheetprovided with this bulge is brought by embossing into the form of thethickened annular region serving as a stopper (see FIGS. 5A to 5D of DE10 2006 021 499 A1). In this embodiment the region of the steel sheetprovided with the bulge thus forms a sort of blank of the thickenedannular region to be produced and serving as a stopper, and once thisblank has been deformed by embossing, specifically by compressionperpendicularly to the plane of the further sealing layer, and has beenbrought into the form of the thickened annular region serving as astopper, said thickened annular region on the side thereof correspondingto the concave side of the bulge forming the blank has a functionless,only slight annular indentation surrounding the combustion chamberopening and therefore has a substantially rectangular cross section, ofwhich the thickness is greater than that of the further sealing layer,which is flat for the rest and has the same thickness everywhere, i.e.the original thickness of the steel sheet used for the further sealinglayer.

In the case of the cylinder head gaskets presented by DE 10 2006 021 499A1, the further sealing layer arranged between the two functional layersthus has, in the region of the combustion chamber opening, just a singlethickened annular region serving as a stopper, which thickened annularregion is arranged, relative to the combustion chamber opening, radiallyinside the sealing beads of the two functional layers for which thethickened annular region performs a stopper function.

Particularly when, with the flat gasket according to the invention, thesealing bead is in the shunt pressure path, the second sealing layer ispreferably formed such that the width of the annular groove is greaterthan the width of the sealing bead so that the latter, when the gasketis installed and/or in sealing operation, cannot be damaged by the edgesof the annular groove. In this respect it is also advantageous when theside walls of the annular groove at the upper, free edges thereof arerounded (in a cross section through the second sealing layer), i.e. areprovided with a radius. As will also become clear from the following,the width of the annular groove however may also be the same size as orsmaller than the width of the sealing bead. In addition, the above isalso true for the case of a sealing bead in what is known as the mainpressure path, for which it may be recommended to select the width ofthe annular groove so as to be smaller than the width of the sealingbead.

Irrespective of whether the sealing bead is in the shunt or mainpressure path in the case of the flat gasket according to the invention,it is recommended to form the flat gasket such that the depth of theannular groove is dimensioned such that when the flat gasket is pressedand when a functional layer bears in sealing operation on each side ofthe annular groove against the at least one thickened annular region,the sealing bead is deformed at least substantially only reversibly,i.e. elastically. In preferred embodiments of the flat gasket accordingto the invention the radially inner part of the at least one thickenedannular region relative to the media-passage opening servessubstantially to form a portion of increased thickness of the flatgasket in the region thereof directly adjoining the media-passageopening, that is to say in the case of a cylinder head gasket i.e. of aportion of increased thickness, the flat gasket can still be designedsuch that the at least one thickened annular region on both sides of thesealing bead forms a deformation limiter for this, such that the sealingbead is not damaged in sealing operation by excessive flattenedportions.

The invention also relates to a method for producing a metallic flatgasket comprising a sealing plate having at least one media-passageopening, which sealing plate has, in the region of the media-passageopening, at least one spring steel functional layer formed of a firststeel sheet with a sealing bead that surrounds the media-passage openingand is formed as a full bead, and also a second sealing layer, which isdirectly adjacent to the functional layer and is formed of a secondsteel sheet, which is more easily deformable compared with spring steel,which second sealing layer has, around the passage opening, an annularzone adjacent thereto and, radially outwardly adjacently to said annularzone relative to the media-passage opening, has an original thickness ofthe second steel sheet, wherein the second sealing layer in its annularzone has at least one annular region that is thickened compared with theoriginal thickness of the second sheet steel, which thickened annularregion extends along the sealing bead in a plan view of the sealingplate and on the side of the second sealing layer facing towards thefunctional layer forms an annular groove, in which the sealing beadengages with its bead crest when the flat gasket is pressed; inaccordance with the invention, in order to produce the thickened annularregion, a temporary passage opening concentric with the media-passageopening to be produced in the second steel sheet used for the secondsealing layer is made in said second steel sheet, the diameter of saidtemporary passage opening being smaller than that of the media-passageopening, whereupon the second steel sheet is compressed from the edge ofthe temporary through-opening and in so doing undergoes an enlargementof its material thickness, such that a blank of the thickened annularregion is produced, and this blank is brought by embossing into the formof the thickened annular region.

Alternatively, in order to produce a thickened annular region, atemporary passage opening concentric with the media-passage opening tobe produced in the second steel sheet used for the second sealing layercan be made in said second steel sheet, the diameter of said temporarypassage opening being smaller than that of the media-passage opening,whereupon a bulge surrounding the temporary passage opening in anannular fashion is impressed into the second steel sheet such that herethe outer edge of the temporary passage opening is drawn radiallyoutwardly, whereupon the region of the second steel sheet provided withthe bulge is brought by embossing into the form of the thickened annularregion.

If the second sealing layer has only one thickened annular region, theannular groove is impressed into this thickened annular region inpreferred embodiments of the method according to the invention.

If two thickened annular regions are produced in the second steel sheetby means of one and/or the other embodiment of the method according tothe invention, preferably one behind the other and spaced apart from oneanother radially relative to the media-passage opening, these form theannular groove between them; in this case it is recommended to configurethe production method such that the radially inner thickened annularregion relative to the media-passage opening is produced by compressionof the second steel sheet and the radially outer thickened annularregion is produced by embossing of a bulge (in each case with asubsequent embossing of the deformed region of the second steel sheetsin order to provide this region with the form of the thickened annularregion). However, it may also be advantageous to produce each of thethickened annular regions by embossing of a bulge and subsequentembossing of the deformed region of the second steel sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, details and advantages of the flat gasket according tothe invention and of the production method according to the inventionwill emerge from the accompanying drawings of some embodiments of theinvention and also the following description of these embodiments; inthe drawings

FIG. 1: shows a plan view of part of a flat gasket according to theinvention formed as a cylinder head gasket;

FIG. 2A shows a heavily simplified and schematized sectionalillustration of a first embodiment of the invention, more specifically asection along the line 2-2 in FIG. 1;

FIGS. 2B to 2D: show sectional illustrations corresponding to FIG. 2A ofa second, third and fourth embodiment of the invention;

FIGS. 3A to 3D: show an illustration of a number of steps of a methodaccording to the invention for producing the inner layers shown in FIGS.2B to 2D of a cylinder head gasket according to the invention, of whichthe inner layer for a combustion chamber opening has only a singlethickened annular region, into which on both sides an annular groove isimpressed for the sealing bead of the respective adjacent functionallayer; and

FIGS. 4A to 4D: show illustrations corresponding to FIGS. 3A to 3D of anumber of steps of a method according to the invention for producing theright thickened annular region according to FIG. 2A of the inner layerof the cylinder head gasket shown in FIG. 2A.

DETAILED DESCRIPTION OF THE INVENTION

A multi-layer cylinder head gasket according to the invention butillustrated only in part in FIG. 1 in a plan view has a sealing plate 10comprising an upper functional layer 12 (visible in FIG. 1), a pluralityof combustion chamber openings 14, and a plurality of screw holes 16 forthe passage of cylinder head screws.

Sealing beads 18 are impressed into the upper functional layer 12, andalso into a lower functional layer not visible in FIG. 1, each of whichsealing beads surrounds a combustion chamber opening 14 and is arrangedat a radial spacing from the edge of the associated combustion chamberopening. The sealing beads 18 are formed as what are known as full beadswith a cross section that in particular is shaped approximately in theform of the arc of a circle, wherein FIG. 1 is to represent a plan viewof the concave side of each sealing bead.

In the narrow web regions of the sealing plate 10 between mutuallyadjacent combustion chamber openings 14, the sealing beads 18 transitioninto one another, as is illustrated in FIG. 1, such that two mutuallyadjacent sealing beads 18 in each of these web regions form only asingle bead portion 18 a—it is also possible, however, in principle fortwo mutually adjacent sealing beads 18 to be separated from one anotherin each of these web regions such that each of these sealing beads formsan annulus which is closed per se, which presupposes that the web regionhas a width sufficient for this purpose.

The section along line 2-2 in FIG. 1 shown in FIG. 2A through a firstembodiment of the cylinder head gasket according to the invention shows,apart from the upper functional layer 12 with its sealing bead 18, alsoa lower functional layer 20 with a sealing bead 22 and also an innerlayer 24, which is arranged between these two functional layers andwhich is the second sealing layer in the sense of the accompanyingclaims. A steel sheet formed from a relatively easily deformable, i.e.relatively ductile, steel has been used for the inner layer 24, and theinner layer 24 has an annular zone around the combustion chamber opening14 with a radial width B1, wherein this annular zone directly bordersthe outer edge of the combustion chamber opening 14. This annular zoneitself will also be designated hereinafter by B1.

In accordance with the invention the steel sheet used for the innerlayer 24 has been deformed such that it has two thickened annularregions B2 and B3 around the combustion chamber opening 14, whichannular regions are arranged at a radial spacing B4 from one anotherrelative to an axis 14 a of the combustion chamber opening 14 and therespective radial width of which annular regions will be designatedhereinafter likewise by B2 and B3 respectively. The radially outerthickened annular region B3 ends at the radially outer edge of theannular zone B1, and the radially inner thickened annular zone B2 endsat the radially inner edge of the annular zone B1.

Between the thickened annular regions B2 and B3, the inner layer 24 oneach of the two sides thereof thus forms an annular groove 30 and 32running around the combustion chamber opening 14.

Radially outwardly adjacently to the annular zone B1 and in the regionhaving the width B4 between the two thickened annular regions B2 and B3,the inner layer 24 has a thickness and a hardness corresponding at leastsubstantially to the original thickness and the original hardness of thesteel sheet used for production of the inner layer 24; by contrast, thethickened annular regions B2 and B3 have a greater thickness than theoriginal thickness of this steel sheet, but also a greater hardness thanthe original hardness of this steel sheet, wherein this greater hardnessis to be attributed to the fact that the thickened annular regions B2and B3 have each been produced by a cold-forming of the steel sheet usedfor the inner layer 24 and this deformation was accompanied by a strainhardening of the steel, on account of which the thickened annularregions B2 and B3 have a greater hardness than the original hardness ofthe steel sheet used for the production of the inner layer 24.

In the case of the cylinder head gasket according to the inventionillustrated in FIG. 2A, the sealing beads 18 and 22 protruding towardsthe inner layer 24 are arranged opposite one another and opposite theregion of the inner layer 24 having the width B4 located between thethickened annular regions B2 and B3, and the radial width of the sealingbeads 18 and 22 relative to the axis 14 a is at most of identical sizeand preferably slightly smaller than the width B4. Furthermore, inpreferred embodiments the radial width of the annular zone B1 is at mostapproximately twice the radial distance of the bead crests, designatedby 18 a and 22 a, of the sealing beads 18 and 22 from the outer edge ofthe combustion chamber opening 14 (always in relation to the axis 14 a).

In accordance with the description still to follow, however, the radialwidth of the sealing beads 18 and 20 also may be slightly greater thanthe width B4. In addition, it is recommended, at the radially inner andradially outer edge of each annular groove 30, to round off thethickened annular regions B2 and B3 at the transitions into theirsurfaces facing the functional layer 12 and the functional layer 20,such that they have no edges there, in contrast to the illustration inFIG. 2A (the same may apply where applicable to the radially inner endof the thickened annular region B2 and/or to the radially outer end ofthe thickened annular region B3). It is even more advantageous to formthe inner layer 24 in the region of the annular groove 30 and/or of theannular groove 32 such that the cross section of the annular groove inquestion has a rounded portion or a radius at the transition of thegroove side walls into the groove base (instead of the angularcross-sectional shape shown in FIG. 2A).

FIG. 2A shows the cylinder head gasket according to the invention in theunpressed state, wherein the spacings of the functional layers 12 and 20from the inner layer 24, measured in the direction of the axis 14 a,have been illustrated with exaggerated size. In accordance with theinvention the heights to be measured in the direction of the axis 14 aof the as yet unpressed sealing beads 18 and 22 are greater than thedepths of the annular grooves 30 and 32 measured in this direction,wherein these heights and depths are to be dimensioned and matched toone another in accordance with the invention such that, when thecylinder head gasket is pressed and when functional layers 12 and 20bear on both sides of the annular grooves 30 and 32 against thethickened annular regions B2 and B3, the sealing beads 18 and 22 areflattened at least substantially only reversibly, i.e. are elasticallydeformed (apart from a slight plastic deformation, which may or may notbe present, when the gasket is installed).

In FIG. 2B the illustration corresponding to FIG. 2A of a secondembodiment of the cylinder head gasket according to the invention willonly be described hereinafter insofar as it differs from the embodimentaccording to FIG. 2A, and where possible the same reference signs asused in FIG. 2A have been used in FIG. 2B, but with the addition of adash.

Furthermore, it is noted that preferred methods according to theinvention for producing the inner layer of the cylinder head gasketillustrated in FIG. 2B will be described with reference to FIGS. 3A to3D and FIGS. 4A to 4D.

In FIG. 2B a lower functional layer corresponding to the functionallayer 20 of the embodiment according to FIG. 2A has been omitted for thesake of clarity, although the inner layer 24′ has annular grooves 30′and 32′ between thickened annular regions B2′ and B3′ for two functionallayers arranged on each of the two sides of said inner layer. In theembodiment shown in FIG. 2B, these two annular grooves have the samewidth, which is larger than the width of the adjacent sealing bead(wherein only one of the sealing beads, specifically the sealing bead18′, has been illustrated), and the two annular grooves 30′ and 32′ arearranged opposite one another (in the direction of the axis of theadjacent combustion chamber opening 14′). As shown in FIG. 2B, the crosssection of each of the annular grooves 30′ and 32′ is formed in thisembodiment such that it is rounded in the regions of the two groove sidewalls, more specifically both at the transition into the groove base,but also particularly at the transition into those surfaces of the twothickened annular regions B2′ and B3′ that abut against the adjacentfunctional layers when the gasket has been installed; an edge pressurebetween the functional layers and the thickened annular regions isavoided in this way (by contrast with a design according to FIG. 2A).FIG. 2B also shows an annular groove 64′, which results from theproduction method yet to be described on the basis of FIGS. 3A to 3D.

The embodiments according to FIGS. 2C and 2D differ from the embodimentaccording to FIG. 2B only in the following manner (which is why the samereference signs have been used in all of these three Figures).

In FIG. 2C only the inner layer 24′ has been illustrated, of which theannular grooves 30′ and 32′ are formed in the same way as in theembodiment according to FIG. 2B, but in the embodiment according to FIG.2C these annular grooves are offset from one another in the radialdirection relative to the axis of the adjacent combustion chamberopening 14′, such that they only overlap one another in a plan view ofthe inner layer 24′. Consequently, the associated sealing beads of thetwo functional layers accommodating the inner layer 24′ between themmust be offset from one another in the same way.

Apart from the fact that FIG. 2D shows two functional layers 12′ and20′, FIG. 2D differs from FIG. 2B only as follows.

Whereas, similarly to the embodiment according to FIG. 2B, the annulargroove 30′ has a width B4.1 which is greater than the width B18 of thesealing bead 18′, the sealing bead 22′ of the functional layer 20′ has awidth B22 which is greater than the width B4.2 of the annular groove32′—this allows the annular groove 32′ on account of its cross-sectionalshape, which is rounded at the groove side walls, to avoid experiencingedge pressure in the region of the sealing bead 22′ of the functionallayer 20′.

When producing the three embodiments of the inner layer 24′ illustratedin FIGS. 2B to 2D, an approach is preferably adopted such that the innerlayer 24′ is firstly deformed by cold-forming, such that it has a singlethickened annular region, from which the two thickened annular regionsB2′ and B3′ are formed by impressing the annular grooves 30′ and 32′.Due to the forming and embossing process, the inner layer 24′ has ahardness, both in the two thickened annular regions B2′ and B3′ and inthe region between the two annular grooves 30′ and 32′, that is greaterthan the original hardness of the steel sheet used for the production ofthe inner layer 24′. Since a single thickened annular region is firstlyproduced by cold-forming, into which the two annular grooves 30′ and 32′are then impressed, the inner layer 24′, in its region located betweenthese two annular grooves, has an even greater hardness there, onaccount of the further cold-forming and an accompanying strain hardeningof this region, than in the two thickened annular regions B2′ and B3′.It must also be stressed that the above statements also apply to amodified inner layer, adjacently to which only a single functional layeris formed and which consequently has only an annular groovecorresponding to the annular groove 30′ or the annular groove 32′. Forthe rest, the same as for the annular zone B1 of the inner layer 24 ofthe gasket illustrated in FIG. 2A is true for the embodiments accordingto FIGS. 2B to 2D in respect of their thickened annular region B1′indicated only in FIG. 2B, their thickened annular regions B2′ and B3′,and the annular grooves 30′ and 32′.

FIG. 3A shows part of a steel sheet 50, from which the inner layer 24′of the gaskets shown in FIGS. 2B to 2D can be produced and which isinitially flat and smooth, before it is shaped by deformation, as shownin FIG. 3A. Here, the part of the steel sheet 50 from which the part ofthe inner layer 24′ shown in FIGS. 2B to 2D is produced is illustratedin FIG. 3A.

In a method step not illustrated in the drawings, a temporary passageopening is firstly punched out from the steel sheet 50 and later formsthe combustion chamber opening 14′ of the inner layer 24′—the edge ofthe steel sheet 50 running around the temporary passage opening when theflat steel sheet 50 is still whole has been designated in FIG. 3A by 50a.

The left region of the steel sheet 50 according to FIG. 3A is thenclamped at a radial spacing from the temporary passage opening between atool upper part 52 and a tool lower part 54, such that this region ofthe steel sheet 50 cannot move, more specifically not even in thehorizontal direction according to FIG. 3A, whereupon a bead-like bulge56 surrounding the temporary passage opening in annular fashion isimpressed into the steel sheet 50, more specifically by means of anembossing tool 58 movable vertically from bottom to top in accordancewith FIG. 3A and by means of a hold-down device 60, which is stationaryduring the embossing process. During the course of the embossing of thebulge 56, the edge 50 a of the steel sheet 50 according to FIG. 3A isdrawn to the left and a larger passage opening correspondingapproximately to the combustion chamber opening 14′ is thus producedfrom the temporary passage opening.

In a next method step illustrated in FIG. 3B, in which the embossingtool 58 and the hold-down device 60 have no involvement, an annulargroove 64 is impressed into the upper side of the steel sheet 50 at theradially outer edge of the bulge 56 by means of an embossing tool 62,said annular groove surrounding the through-opening of the steel sheet50.

In a further method step illustrated in FIG. 3C, on the one hand thesteel sheet 50 is secured radially outside the bulge 56 with the aid ofits annular groove 64 and of the embossing tool 62, and on the otherhand the bulge 56 is compressed and flattened in the vertical direction,more specifically with the aid of an embossing tool 68 movable in thevertical direction and with the aid of an abutment 70. In this way, athickened annular region 72 shown in FIG. 3C is produced from the bulge56, which thickened annular region protrudes on both sides beyond theundeformed region of the steel sheet 50 (in the illustrated embodimentthe protrusion above is much greater than below) and has smooth endfaces parallel to one another above and below, which also extendparallel to the two main surfaces of the undeformed region of the steelsheet 50.

The embossing tool 68 is shaped and dimensioned such that, when thebulge 56 is compressed and flattened, i.e. when the bulge 56 is deformedinto the thickened annular region 72, the latter adopts a shape andposition such that the edge 50 a transitions into the edge of thecombustion chamber opening 14′.

As can be seen in FIG. 3C, the thickened annular region 72 on theunderside thereof also has a small and flat annular groove 74, whichruns around the combustion chamber opening 14′; the reason for thepresence of this annular groove is considered to be the fact that whenthe bulge 56 is compressed and flattened the concave side thereof is notlevelled completely.

In contrast to that illustrated in FIG. 3C, instead of the embossingtool 68 and the abutment 70, two tool parts may also be provided, ofwhich the upper serves only to flatten the bulge 56 and of which thelower, however, serves not only as an abutment for the process offlattening the bulge 56, but also has a region displaceable upwardly inthe vertical direction in accordance with FIG. 3C with a beveled surfacethat abuts against the edge 50 a and when displaced upwardly enlargesthe passage opening provided in the steel sheet 50 and in so doing leadsover the course of the production of the annular region 72 to anadditional thickening there of the steel sheet and at the same timecalibrates the diameter of the combustion chamber opening 14′.

In a last step of the production method, illustrated in FIG. 3D, annulargrooves 84 and 86 are impressed into the thickened annular region 72 bymeans of two embossing tools 80 and 82 on the upper side and theunderside of said region, such that the thickened annular region B1′ ofthe inner layer 24′ illustrated in FIG. 2B is produced.

If necessary, the inner layer 24′ may also then be punched in order toproduce the combustion chamber opening 14′ with its final diameter.

It should also be noted that the method described on the basis of FIGS.3A to 3C can also be used in principle for a separate production of anyof the thickened annular regions B2 and B3 of the gasket according toFIG. 2A (then the step described on the basis of FIG. 3D of producingthe two annular grooves 84 and 86 is omitted).

Lastly, with reference to FIGS. 4A to 4D, a method will be describedwith which a thickened annular region can be produced similarly to theannular region 72 illustrated in FIG. 3C, into which the annular grooves84 and 86 shown in FIG. 3D are then also impressed, by means of which,however, the radially inner thickened annular region B2 of theembodiment according to FIG. 2A or a thickened annular zone analogous tothe annular zone B1′ of the embodiment according to FIG. 2B can beproduced, wherein in the latter case as well annular groovescorresponding to the annular grooves 30′ and 32′ then still have to beimpressed.

FIG. 4A shows a steel sheet 100 with a left undeformed region inaccordance with FIG. 4A and a free, right edge 100 a of a temporarypassage opening produced in the steel sheet 100 and adjoined radiallyoutwardly, i.e. to the left in accordance with FIG. 4A, by an annularzone 102, which, by contrast with that illustrated in FIG. 4A, isinitially flat and smooth and transitions continuously into the leftregion of the steel sheet 100 in accordance with FIG. 4A.

The left region of the steel sheet 100 according to FIG. 4A not to bedeformed is clamped, as shown in FIG. 4A, between clamping jaws 104 and106, whereupon a profile is impressed into the annular zone 102 using anupper and a lower tool part 108 and 110 respectively of an embossingtool, the cross section of said profile being similar to a flat W andtransitioning via a cross-sectional tapering 112 into the clamped regionof the steel sheet 100. The cross-sectional profile of the annular zone102 thus has a bulge 114 and two upwardly inclined limbs 114 a and 114b.

In a method step not illustrated in the drawings the annular zone 102 isbent upwardly about the cross-sectional tapering 112 through 90°, suchthat a preliminary stage of the form of the steel sheet 100 shown inFIG. 4B is created. The lower clamping jaw 106 according to FIG. 4A isthen shifted slightly to the right, such that it assumes the positionillustrated in FIG. 4B. By means of a punch 120 shown in FIG. 4B, theannular zone 102 is then compressed transversely to the longitudinalextent thereof, specifically by displacing the punch 120 downwards intothe position illustrated in FIG. 4B; the material thickness of the steelsheet 100 in the region of the annular zone 102 is thus increased, butsince the latter is trapped between the punch 120 and the clamping jaw104, the steel sheet of the annular zone 102 cannot warp or bulgeconsiderably in the horizontal direction according to FIG. 4B.

The envisaged increase of the material thickness of the steel sheet 100in the region of the annular zone 102 presupposes, however, that thesteel sheet 100, prior to the displacement of the punch 120 according toFIG. 4B downwards between said punch and the clamping jaw 104, has aclearance necessary for the desired material thickness increase; as aresult of this, the steel sheet 100 in the region of the annular zone102 warps slightly over the course of the material thickness increase,i.e. the compression of the steel sheet, as has been indicated in FIG.4B. Due to the profiling of the annular zone 102 illustrated in FIG. 4A,the steel sheet 100 in the event of compression of the annular zone 102warps or ripples at points predefined by this profiling. It has now beenshown that, during the course of the above-described compression of thesteel sheet 100 in the annular zone 102 thereof and the accompanyingwarping, the material of the steel sheet 100 flows in regions such thatit is advantageous to slightly offset from one another the annulargrooves 30′ and 32′ shown in FIGS. 2B to 2D, similarly to theillustration in FIG. 2D.

As illustrated in FIG. 4C, the annular zone 102 is pivoted downwardsagain about the cross-sectional tapering 112 by means of a punch 122 andis then compressed between two tool parts 124 and 126 shown in FIG. 4Din a direction perpendicular to the undeformed region of the steel sheet100, such that a compact thickened annular region 130 is created, whichmay correspond to the thickened annular region B2 of the embodimentaccording to FIG. 2A. As shown in FIG. 4D, the cross section of thethickened annular region 130 corresponds approximately to a rectangle,and the thickness of this thickened annular region is much greater thanthe thickness of the original steel sheet 100.

Similarly to the production method described with reference to FIGS. 3Ato 3D, in the method according to FIGS. 4A to 4D the edge 100 a definingthe combustion chamber opening 14 or 14′ at the end moves with themethod steps shown in FIGS. 4A to 4B in the direction of the undeformedregion of the steel sheet or of the sealing layer, such that a largerfinal media-passage opening or combustion chamber opening is providedfrom a temporary passage opening initially formed in the steel sheet.

All embodiments therefore have the common feature that the material forproducing the least one thickened annular region of a flat gasketaccording to the invention is recovered from the free end of the secondsteel sheet used for the inner layer or the second sealing layer, saidfree end defining the temporary passage opening produced initially.

A key advantage or an essential feature of the invention also lies inthe fact that the radially inner and the radially outer stopper of adouble stopper according to the invention may readily have differentthicknesses or heights and/or one of the stoppers or both stoppers mayhave a height profile or different height profiles respectively, sincefor this purpose only the embossing tool 68 or at least one of theembossing tools 80 and 82 or at least one of the tool parts 124 and 126has to be correspondingly configured.

1. A metallic flat gasket comprising a gasket plate having at least onemedia-passage opening and having, in the region of the media-passageopening, at least one spring steel functional layer formed of a firststeel sheet with a sealing bead that surrounds the media-passage openingand is formed as a full bead with a bead crest arranged between two beadfeet, and also a second gasket layer, which is directly adjacent to thefunctional layer and is formed of a second steel sheet, which is moreeasily deformable compared with spring steel, which second gasket layerhas, around the media-passage opening, an annular zone adjacent theretoand, radially outwardly adjacently to said annular zone relative to themedia-passage opening, has an original thickness and an originalhardness of the second steel sheet, wherein the second gasket layer inits annular zone has at least one annular region that is thickenedcompared with the original thickness of the second steel sheet, whichthickened annular region extends along the sealing bead in a plan viewof the gasket plate and on the side of the second gasket layer facingtowards the functional layer forms an annular groove, in which thesealing bead engages with its bead crest when the flat gasket ispressed, wherein the second gasket layer in the thickened annular regionproduced by deforming areas of the second steel sheet has a greaterhardness, based on a strain hardening in said areas of the second steelsheet on account of the deformation, than the original hardness of thesecond steel sheet, and wherein (a) the annular zone has only onethickened annular region, into which an annular groove is impressed onat least one side of the second gasket layer, or (b) the annular zonehas, in the radial direction relative to the media-passage opening, twothickened annular regions arranged one behind the other and spaced apartfrom one another which form the annular groove between them.
 2. The flatgasket according to claim 1, in which the second gasket layer isarranged directly between two spring steel functional layers, each ofwhich has a sealing bead surrounding the media-passage opening, whereinthe least one thickened region forms an annular groove on each side ofthe second gasket layer, and when the flat gasket is pressed the sealingbeads engage with their sealing crests in these annular grooves.
 3. Theflat gasket according to claim 2, wherein, in a section through thegasket plate along a plane containing the axis of the media-passageopening, the annular grooves of the two layer sides are offset from oneanother in the radial direction relative to this axis, and in that thesealing beads of the two functional layers are offset from one anotherin the same manner.
 4. The flat gasket according to claim 3, wherein, ina plan view of the gasket plate, the annular grooves provided on the twolayer sides overlap one another.
 5. The flat gasket according to claim1, in which the second gasket layer, between the two mutually spacedthickened annular regions, has at least approximately the originalthickness and the original hardness of the second steel sheet.
 6. Theflat gasket according to claim 1, in which the at least one thickenedannular region on both sides of the second gasket layer protrudes beyondthe region of the second gasket layer radially outwardly bordering theannular zone.
 7. The flat gasket according to claim 1, in which theradial width of the annular zone relative to the media-passage openingis at most approximately twice the radial spacing of the bead crest fromthe outer edge of the media-passage opening.
 8. The flat gasketaccording to claim 1, in which the thickened annular region extends asfar as the outer edge of the media-passage opening.
 9. The flat gasketaccording to claim 1, in which the width of the annular groove is thesame size as or larger than the width of the sealing bead associatedwith this annular groove.
 10. The flat gasket according to claim 9, inwhich the depth of the annular groove is dimensioned such that, when theflat gasket is pressed and when a functional layer bears in sealingoperation on each side of the annular groove against the at least onethickened annular region, the sealing bead is deformed exclusivelyreversibly, i.e. elastically.
 11. A method for producing a metallic flatgasket comprising a gasket plate having at least one media-passageopening and having, in the region of the media-passage opening, at leastone spring steel functional layer formed of a first steel sheet with asealing bead that surrounds the media-passage opening and is formed as afull bead, and also a second gasket layer, which is directly adjacent tothe functional layer and is formed of a second steel sheet, which ismore easily deformable compared with spring steel, which second gasketlayer has, around the passage opening, an annular zone adjacent theretoand radially outwardly adjacently to said annular zone relative to themedia-passage opening, has an original thickness of the second steelsheet, wherein the second gasket layer in its annular zone has at leastone annular region that is thickened compared with the originalthickness of the second sheet steel, which thickened annular regionextends along the sealing bead in a plan view of the gasket plate and onthe side of the second gasket layer facing towards the functional layerforms an annular groove, in which the sealing bead engages with its beadcrest when the flat gasket is pressed, wherein, in order to produce thethickened annular region, a temporary passage opening concentric withthe media-passage opening to be produced in the second steel sheet usedfor the second gasket layer is made in said second steel sheet, thediameter of said temporary passage opening being smaller than that ofthe media-passage opening, whereupon the second steel sheet iscompressed from the edge of the temporary through-opening, such that ablank of the thickened annular region is produced, and this blank isbrought by embossing into the form of the thickened annular region. 12.A method for producing a metallic flat gasket comprising a gasket platehaving at least one media-passage opening and having, in the region ofthe media-passage opening, at least one spring steel functional layerformed of a first steel sheet with a sealing bead that surrounds themedia-passage opening and is formed as a full bead, and also a secondgasket layer, which is directly adjacent to the functional layer and isformed of a second steel sheet, which is more easily deformable comparedwith spring steel, which second gasket layer has, around the passageopening, an annular zone adjacent thereto and, radially outwardlyadjacently to said annular zone relative to the media-passage opening,has an original thickness of the second steel sheet, wherein the secondgasket layer in its annular zone has at least one annular region that isthickened compared with the original thickness of the second sheetsteel, which thickened annular region extends along the sealing bead ina plan view of the gasket plate and on the side of the second gasketlayer facing towards the functional layer forms an annular groove, inwhich the sealing bead engages with its bead crest when the flat gasketis pressed, wherein, in order to produce the thickened annular region, atemporary passage opening concentric with the media-passage opening tobe produced in the second steel sheet used for the second gasket layeris made in said second steel sheet, the diameter of said passage openingbeing smaller than that of the media-passage opening, whereupon a bulgesurrounding the temporary passage opening in an annular fashion isimpressed into the second steel sheet such that hereby the outer edge ofthe temporary passage opening is drawn radially outwardly, and theregion of the second steel sheet provided with the bulge is brought byembossing into the form of the thickened annular region.
 13. The methodaccording to claim 11, in which the annular groove is impressed into thethickened annular region.
 14. The method according to claim 12, in whichthe annular groove is impressed into the thickened annular region. 15.The method according to claim 11, in which two thickened annular regionsare produced in the second steel sheet at a radial spacing from oneanother relative to the media passage opening, which annular regionsaccommodate the annular groove between them.
 16. The method according toclaim 12, in which two thickened annular regions are produced in thesecond steel sheet at a radial spacing from one another relative to themedia passage opening, which annular regions accommodate the annulargroove between them.
 17. The method according to claim 15, wherein theradially inner thickened annular region relative to the media-passageopening is produced in accordance with claim 11 and the radially outerthickened annular region is produced in accordance with claim
 12. 18.The method according to claim 16, wherein the radially inner thickenedannular region relative to the media-passage opening is produced inaccordance with claim 11 and the radially outer thickened annular regionis produced in accordance with claim
 12. 19. The method according toclaim 15, wherein both thickened annular regions are produced inaccordance with claim
 12. 20. The method according to claim 16, whereinboth thickened annular regions are produced in accordance with claim 12.